A film scanner capable of high definition television (HDTV) resolution preferably includes a standards converter in its signal processing to convert from the film scanning standards employed by the film scanner to HDTV standards or to conventional 625/525 line (PAL/NTSC) standards. The general function employed is that of interpolation, that is, the number of output samples is a computed (lesser/greater) function of the number of the input samples. More particularly, the specific function employed to convert to lower definition is that of decimation, that is, a reduction in the number of output samples compared to input samples.
High speed finite impulse response (FIR) filter processers have been disclosed in configurations permitting decimation, interpolation, adaptive filtering, and two dimensional filtering (e.g., see the L64260/L64261 High Speed Versatile FIR Filter (VFIR), produced by LSI Logic Corporation, which also may be configured to permit the filter coefficients to change at the same rate as the input data). Such filters calculate a computational algorithm in a plurality of computational stages arranged in parallel with the outputs thereof summed to form the output of the filter (e.g., the L64260/L64261 has four stages each with a high speed MAC and four data and four coefficient registers).
When an FIR filter processor is used in the digital signal processing channel of a film scanner to convert from higher to lower definition, the decimation factor is rarely an integer. This places special demands on the horizontal FIR function as the filter coefficients need to be changed at the input data rate, i.e., for an image input, at the pixel rate. On top of that requirement, the interpolation (decimation) parameters must be programmable to accommodate the various input film formats and output television standards. In addition, a scanner application should include the facility for pan and zoom to accommodate the translation between the scanned film format and the 16:9 HDTV or 4:3 625/525 (PAL/NTSC) line aspect ratio. This requires varying interpolator (decimation) characteristics field by field for different zoom and pan ratios.